1. Field of the Invention
The present invention generally relates to a method for transmitting information to a plurality of mobiles from an antenna array.
2. Description of the Related Art
In communication networks and, in particular, in wireless communication networks there is a need to increase the overall capacity of the network. The overall capacity of a network relates the number of subscribers that can be served by the network and the amount of information each such subscriber can convey (i.e., transmit and/or receive) at any particular time. Service providers, who are entities that own, operate and control system equipment used in a communication network, are constantly challenged by their subscribers to provide more communication channels and to increase the amount of information each such channel can transmit and/or receive at any particular instant of time.
The service providers are therefore constantly searching for methods and equipment that can meet the changing needs of their subscribers. Subscribers of communication networks, including wireless communication networks, require higher information throughput in order to exploit the expanding range of services being provided by current communication networks. For example, wireless communication subscribers are now able to have simultaneous access to data networks such as the Internet and to telephony networks such as the Public Switched Telephone Network (PSTN). Service providers are constantly investigating new techniques that would allow them to increase their information throughput. Information throughput is the amount of informationxe2x80x94usually measured in bits per secondxe2x80x94successfully conveyed over a communication channel. Information throughput can be increased in a number of well known manners. One way is by increasing the power of the transmitted signals. A second way is by expanding the frequency range (i.e., bandwidth) over which the communication is established. However, both power and bandwidth are typically limited by governmental and standards organizations that regulate such factors. In addition, for portable devices, power is limited by battery life.
An approach which circumvents the power and bandwidth limitations is to increase the number of antennas used to transmit and receive communication signals. Typically, the antennas are arranged as an array of antennas. One techniques used by service providers is commonly referred to as a MIMO (Multiple Input Multiple Output) technique. In a MIMO configuration, the antenna array is coupled to a signal processing device and the combination is used to transmit and/or receive multiple distinct signals. One example of a MIMO system is the BLAST (Bell Labs Layered Space Time) system conceived by Lucent Technologies headquartered in Murray Hill, N.J. In a MIMO configuration such as BLAST, all of the antennas of the array are used to either transmit or receive information to or from a subscriber at a particular instant of time. Typically, the subscriber equipment or mobile (e.g., cellular phone, wireless laptop, Personal Digital Assistant (PDA)) is also equipped with an antenna array that is used to transmit or receive information from system equipment (e.g., cell site or base station).
Although a MIMO configuration is helpful in increasing the information throughput of a particular communication channel, it does not necessarily help increase the number of subscribers that can adequately use the communication network. For example, the antenna array at a base station implementing the MIMO technique would cause all or a plurality of antennas of the antenna array to simultaneously transmit (or receive) information to a cellular phone being used by a subscriber. Thus, the array is used by only one subscriber at any particular time and does not serve to increase the number of subscribers that can use the system at any one time. Also, certain antennas in the antenna array at the base station may not be the most appropriate antenna for conveying information to certain subscribers at certain times. It is well known that channel conditions vary from one instant of time to another and many times such conditions adversely affect communications between a subscriber and a base station. Therefore, even though a plurality of antennas is being used to convey information, some of these antennas may not be conveying information successfully thereby reducing the efficiency of the antenna array. The efficiency of the antenna array is the ratio of the amount of information that is actually conveyed to the amount of information that the antenna array is designed to convey.
What is therefore needed is a method that uses antenna arrays of a communication network in such a manner so as to increase the number of subscribers using the communication network. What is also needed is a method of employing an antenna array to convey information to a plurality of subscribers in an efficient manner.
The present invention is a method for conveying information in a communication network using an antenna array where certain of the antennas in the array are coupled to a scheduler such that the number of communication channels used by the network is increased and the antenna is used in an efficient manner. In particular, the method provides an antenna array where certain of the antennas are under the control of a scheduling algorithm residing in the scheduler and each of these antennas is assigned to one or a group subscribers of the communication network. The scheduling algorithm determines when to convey information over a communication channel to a particular corresponding subscriber and accordingly causes the appropriate antenna to convey information to the subscriber for a determined period of time. The scheduling algorithm determines when an antenna is to convey information to a particular subscriber based on channel condition information received by the scheduling algorithm from the subscriber equipment.
The scheduling algorithm allows each antenna under its control to operate in two modes. In the first mode of operation, one or a group of subscribers is pre-assigned to the antennas that are under the control of the scheduling algorithm. The scheduling algorithm then determines when an antenna is allowed to convey information to a pre-assigned subscriber. The scheduling algorithm thus allows the antenna to convey information for any one of the pre-assigned subscribers over its respective communication channel based on channel condition information it receives from its pre-assigned subscribers.
In the second mode of operation, the subscribers of the communication network are not assigned to any particular antenna under the control of the scheduling algorithm. When information associated with a particular subscriber is to be conveyed to that subscriber, the scheduling algorithm selects the most appropriate antenna to convey the information. The scheduling algorithm determines the most appropriate antenna from channel condition information it receives for that particular antenna and the other antennas under its control. In particular, the scheduling algorithm monitors the various channel condition information received from the subscribers and selects the most appropriate antenna for conveying information to a particular subscriber at a particular instant of time. Thus, in this mode of operation, a subscriber is not limited to conveying its information to any particular antenna. Conversely, an antenna under the control of the scheduling algorithm is not limited to convey information to a particular subscriber or group of subscribers.